Previous investigations indicated that each of the dissociation products of H2CO3 destroy tooth enamel producing decay similar, if not the same as, initial caries. The enamel demineralization was rapid at pH 5 indicating predominately H positive actions. Enamel mineral dissolution was slow at pH 7 indicating little H positive action. However, the enamel softened and changed to opaque white appearance in HCO3 solution indicating a significant change in physical and chemical properties of the mineral. These results, and results of others, suggest that the CO2-H2CO3-HCO negative 3-CO 3 negative 2 system in dental plaque and the mineral-water in enamel are a continuum in which distribution and concentrations depend on pH, Pco2, and the diffusibility of the non-ionic CO2 and H2CO3 molecules. The objective of this work is to confirm that dental plaque organisms potentially produce CO2 in amounts to support its diffusion into enamel water where H2CO3 is formed and dissociated to yield locally high concentrations of H positive and HCO negative 3; and that these products dissolve enamel minerals, and leave residual minerals more soluble than enamel. The low levels of fluoride ions known to prevent caries will be studied to determine F negative and carbonic acid system interactions during enamel demineralization and remineralization. The F negative ion effect of increasing the rates of enamel remineralization and of inhibiting dental caries may act synergistically with HCO negative 3 ions. Theoretically, the carbonate containing minerals of enamel contribute to carious processes. The weak acid (pH 5) and chelator (pH 7.4) resistance of enamel carbonates will be tested. Incipient caries of enamel produced by carbonic acid will be studied. The physical changes and chemical composition (Ca, PO4, CO2 and F) of surface minerals of enamel will be determined after reactions in carbonate solutions with and without F negative ions in solutions over the pH range that occurs in dental plaque. BIBLIOGRAPHIC REFERENCES: Phantumvanit, P., Feagin, F.F. and Koulourides, T. Strong and Weak acid sampling for fluoride of enamel remineralized in sodium fluoride solutions. Caries Res. 11:52-61, 1977. Feagin, F.F. and Gray, J.A. Discussion of Remineralization Phenomenon (by L.M. Silverstone). Caries Res. 11:79-83, 1977.